The present invention relates to an image fiber with a mechanism for rotating a field of view which is used, for example, to inspect the inner surface of a pipe for potential damage.
A conventional image fiber with a mechanism for rotating a field of view is shown in FIG. 1. The invention comprises a main portion 5 and a flexible tube 1 in which there is provided in parallel an image fiber 2 and a light guide 3. The ends of the image fiber and the light guide 3 are retained by a cap 4 and the mechanism for rotating a field of view, hereinafter referred to as an adapter 6. The adapter 6 is detachably mounted onto the main portion 5 and is comprised of a motor 7 provided with a rotary shaft which is substantially parallel to the axis of the image fiber 2, a 45.degree. mirror 8 which is arranged in such a way as to be opposite to the ends of the image fiber 2 and the light guide 3 and which is mounted onto the rotary shaft of the motor 7, and a cylindrical transparent window 9 for transmitting therethrough an illuminating light reflected from the mirror 8 and for receiving therethrough an image.
FIG. 1 also shows an object 10 which is illuminated with light from a light source (not shown) via the light guide 3. The image of the object 10 is reflected back to the image fiber 2 through the cylindrical transparent window 9 via the mirror 8 and an image pickup lens 11. If the mirror 8 is rotated by means of the motor 7, as indicated by the arrows in the drawing, it becomes possible to observe the entire inner surface of the pipe. In FIG. 1, reference numeral 12 denotes a nut for adjusting the focus and reference numeral 13 denotes a lock nut for locking the focusing adjustment.
Because the axis 2a of the image fiber 2 differs from the rotational axis 8a of the 45.degree. mirror 8 by .delta., as shown in FIG. 2, the position of the image of the object 10 (the inner surface of a pipe) which is reflected to the image fiber deviates by 2.delta. along the longitudinal direction of the object 10 when the mirror takes positions which are different from each other by 180.degree. (as indicated by the solid and dotted lines in FIG. 2). The above mentioned difference between the axis 2a of the image fiber and the rotational axis 8a of the 45.degree. mirror results from the image fiber 2 and the light guide 3 being symmetrically arranged on both sides of the cylindrical axis of the main portion 5 in order to minimize the outer diameter of the main portion 5.
The nearer the object is with respect to the mirror, for example in pipes with small inner diameters, the more outstanding the deviation of the position of the image of the object becomes. Additionally, there is a further drawback in that because of the reflection of the illuminating light by the transparent window 9 it becomes difficult to view the object.